1. Field of the Invention
The present invention relates to an outboard motor in which a four-stroke-cycle engine is mounted, and more particularly, to an outboard motor having a structure capable of smoothly returning an oil supplied for lubricating the four-stroke-cycle engine into an oil pan.
2. Prior Art
In general, in an outboard motor in a state mounted to a hull of a boat, ship or like, for example, an engine is mounted on the highest portion of the outboard motor with a crankshaft perpendicularly extending therein, the rotation of the crankshaft is transmitted to a propeller shaft through a drive shaft which extends in the downward direction to thereby drive a screw propeller provided at a rear end of the propeller shaft.
When an engine of an outboard motor is of four-stroke-cycle type, an oil pan is provided below the engine, an oil accumulated inside the oil pan is pumped up by an oil pump and supplied into the engine for lubrication and then, the oil flows downward in the engine by gravity and is returned into the oil pan from a plurality of oil-returning holes formed in a lower surface of the engine.
Meanwhile, a plurality of partition walls are provided in a juncture between a cylinder block and a crankcase of the engine so as to separate the cylinders from one another, thereby forming crank chambers as many as the cylinders in number, and the crankshaft is pivotally supported by a crank journal (bearing) formed on each partition wall. Therefore, each partition wall is formed with an oil-passing hole having such a size sufficient to allow the oil to flow downward by the partition wall. The oil passes through the oil-passing hole and drops into the crank chamber and the oil is returned into the oil pan from the lowermost crank chamber through the oil-returning holes of the lower surface of the engine (lower surface of the crankcase).
Conventionally, bottom surfaces of the crank chambers, i.e., the partition walls are set all the same in shape, and the crank chambers are also set all the same in volume.
However, even if the bottom surfaces of the crank chambers are the same in shape and volume, since a great amount of oil flows into the lowermost crank chamber from the upper crank chamber, all the oil is not discharged out from the lower crank chamber and oil tends to be accumulated therein. Furthermore, since the crankshaft rotates in the accumulated oil, there are provided not only a problem that the engine output is dissipated by viscous drag of the oil, but also a problem that oil temperature is increased, or the oil roughly stirred by the crankshaft and atomized issues from a breather exit together with blowby gas.
On the other hand, a flat plate-like member called engine holder to which the engine is mounted is formed with the oil-returning hole for returning the oil flowing down from the engine into the oil pan. In the engine holder, a pair of left and right upper mount units, which are connected to a clamp bracket fixed to a hull, is installed. Since each upper mount unit mainly comprises a rubber damper, in order to prevent the oil from splashing on the upper mount unit, the oil-passing hole can conventionally be formed only at a location away from the upper mount unit, and it is difficult to efficiently return the oil into the oil pan.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide an outboard motor to efficiently return an oil supplied for lubricating an engine, to avoid loss of engine output and temperature increase of the oil and to prevent the oil from issuing from a breather exit together with blowby gas.
This and other objects can be achieved according to the present invention by providing, in one aspect, an outboard motor comprising:
an engine holder;
an engine disposed above the engine holder in mounted usable state of the outboard motor;
an oil pan disposed below the engine holder; and
an engine cover covering the engine holder, the engine and the oil pan;
said engine being an in-line multi-cylinder type and comprising:
a crankcase including a crank chamber in which a crankshaft extends vertically perpendicularly;
a cylinder block disposed rear side of the crankcase; and
a cylinder head disposed rear side of the cylinder block,
wherein the engine includes a plurality of vertically arranged cylinders and a crank chamber of a crank case corresponding to a lowermost cylinder has both shoulder portions each formed by a wall section continuous to a wall section of the lowermost cylinder and extending in a direction normal thereto and another wall section substantially parallel to the wall section of the lowermost cylinder so as to define corner shapes of the shoulder portions to be substantially square in section.
In a preferred embodiment of this aspect, the shoulder portions formed to the lowermost crank chamber and located on a leading side with respect to rotation of the crankshaft is formed with a rib extending upward along an inner wall surface of the crank chamber from a bottom portion thereof. The one shoulder portion located on the leading side of the rotation of the crankshaft is formed, at the bottom portion thereof, with an oil-return hole and the rib is projected within an outline of the oil-return hole.
According to the structure of this aspect, an area of the bottom surface of the lowermost crank chamber and volume of the lowermost crank chamber become greater than those of the upper crank chambers, a large number of oil-return holes can be formed in a bottom surface of the lowermost crank chamber. Therefore, the lowermost crank chamber can accommodate the large amount of oil flowing from the upper crank chambers, and the oil flowing into the lowermost crank chamber can be discharged out efficiently. Therefore, it is possible to prevent the crankshaft from rotating in the oil accumulated in the lowermost crank chamber, to prevent the output loss of the engine and the temperature increase of the oil and to remove detrimental effect that the oil is atomized and issued from the breather exit together with blowby gas.
In the lowermost crank chamber, the flow of oil flowing along a peripheral wall of the crank chamber together with the rotation of the crankshaft is stopped by the rib and guided downward, the oil does not easily remain in the crank chamber.
Furthermore, since the oil stopped by the rib and guided downward is returned into the oil pan through the oil returning hole smoothly, the oil can be returned to the oil pan more effectively.
In another aspect, there is provided an outboard motor comprising:
an engine holder;
an engine which is disposed above the engine holder in a mounted usable state of the outboard motor and which has a crankcase in which a crankshaft extends vertically perpendicularly;
an oil pan disposed below the engine holder; and
a mount unit including upper and lower mount members formed to the engine holder,
wherein the engine holder is formed with a mount fixing portion to which the upper mount member is inserted and fixed in the engine holder, the mount fixing portion having a shaft-hole shape extending horizontally, and an oil-return holes through which an oil returning from the engine passes are formed around the mount fixing portion as viewed in a plan view of the engine.
According to the structure of this aspect, there is no adverse possibility that the oil supplied for lubricating the engine will not splash onto the upper mount unit. Further, since the large number of oil-returning holes can be formed around the upper mount unit, it is possible to return the oil into the oil pan more efficiently.
In a further aspect, there is provided an outboard motor comprising:
an engine holder;
an engine which is disposed above the engine holder in a mounted usable state of the outboard motor and which has a crankcase in which a crankshaft extends vertically perpendicularly;
an oil pan disposed below the engine holder; and
a transmission mechanism disposed to a lower surface side of the engine for transmitting rotation of the crankshaft to a cam shaft, the transmission mechanism including a driven sprocket and a chain,
wherein the engine includes a cylinder head having a lower surface portion to which oil return holes are formed, the oil return holes are located outside of the driven sprocket and the chain of the transmitting mechanism as viewed in a plan view of the engine.
According to the structure of this aspect, oil poured from the oil-return hole of the lower surface of the cylinder head does not splash onto parts which move fast such as a driven sprocket and a chain of a chain transmitting mechanism and does not act as resistance, it is possible to avoid the output loss of the engine.
In a still further aspect, there is provided an outboard motor comprising:
an engine holder;
an engine disposed above the engine holder in a mounted usable state of the outboard motor;
an oil pan disposed below the engine holder; and
an engine cover covering the engine holder, the engine and the oil pan,
the engine being an in-line multi-cylinder type and comprising:
a crankcase including a crank chamber in which a crankshaft extends vertically perpendicularly;
a cylinder block disposed rear side of the crankcase; and
a cylinder head disposed rear side of the cylinder block,
wherein the engine includes a plurality of vertically arranged cylinders and a crank chamber of a crank case corresponding to an uppermost cylinder has both shoulder portions each formed by a wall section continuous to a wall section of the uppermost cylinder and extending in a direction normal thereto and another wall section substantially parallel to the wall section of the uppermost cylinder, the uppermost crank chamber and the cylinder head is communicated through a breather passage which is opened to one of the shoulders of the uppermost crank chamber and the uppermost crank chamber is formed with a rib-shaped peripheral wall rising from an inner surface of the shoulder portion so as to surround the opening of the breather passage.
In this aspect, preferably, the shoulder portions to which breather passage is formed is a shoulder portion of a trailing side one with respect to a rotation of the crankshaft.
According to the structure of this aspect, since the rib-like peripheral wall formed on the opening of the breather passage closer to the crank prevents the oil in the crank chamber from flowing into the breather passage, it is possible to avoid the loss of oil from the breather exit. Furthermore, since the flow of oil flowing along the peripheral wall of the crank chamber together with rotation of the crankshaft does not easily flow into the breather passage, it is possible to avoid the loss of the oil from the breather exit more efficiently.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.